1. Field of the Invention
The present invention relates to Schottky diodes and, more particularly, to a Schottky diode with a control gate for optimization of the on state resistance, the reverse leakage current, and the reverse breakdown voltage.
2. Description of the Related Art
A Schottky diode is a well-known structure with a metal-to-silicon junction that functions as a diode. Schottky diodes have a forward voltage drop that is lower than the forward voltage drop of a conventional pn diode (e.g., 0.35V versus 0.7V) and a switching action that is faster than the switching action of a conventional pn diode (e.g., 100 ps versus 100 ns).
FIGS. 1A-1C show views that illustrate an example of a conventional Schottky diode 100. FIG. 1A shows a plan view, FIG. 1B shows a cross-sectional view taken along line 1B-1B of FIG. 1A, and FIG. 1C shows a cross-sectional view taken along line 1C-1C of FIG. 1A. As shown in FIGS. 1A-1C, Schottky diode 100 includes an n-type semiconductor material 110, such as an n-type substrate, epitaxial layer, or well, and a shallow trench isolation (STI) ring 112 that is formed in semiconductor material 110.
As further shown in FIGS. 1A-1C, Schottky diode 100 includes an n+ ring 114 and a p+ guard ring 116 that are formed in semiconductor material 110 on opposite sides of STI ring 112. Schottky diode 100 also includes a metal ring 120 that touches the top surface of n+ ring 114, and a metal region 122 that touches the top surface of semiconductor material 110 and p+ guard ring 116. Metal ring 120 and metal region 122 are commonly formed with a silicide, such as platinum silicide.
In addition, Schottky diode 100 includes a non-conductive layer 130 that touches the top surfaces of the STI region 112, the metal ring 120, and the metal region 122, a number of first contacts 132 that extend through non-conductive layer 130 to make electrical connections with metal ring 120, and a number of second contacts 134 that extend through non-conductive layer 130 to make electrical connections with metal region 122.
In operation, metal region 122 functions as the anode of the diode and semiconductor material 110 functions as the cathode of the diode. In addition, n+ ring 114 functions as the cathode contact, while p+ guard ring 116 reduces the leakage current. As a result, when the voltage applied to metal region 122 rises above the voltage applied to semiconductor material 110 by approximately 0.35V, a current flows from metal region 122 to n+ ring 114. On the other hand, when the voltage applied to metal region 122 falls below the voltage applied to semiconductor material 110, substantially no current flows from n+ ring 114 to metal region 122.
One of the drawbacks of Schottky diodes is that Schottky diodes have a relatively high reverse leakage current when compared to conventional pn diodes. (The reverse leakage current is a small current that flows when the voltage applied to the anode falls below the voltage applied to the cathode.)
Another drawback of Schottky diodes is that Schottky diodes have a relatively low reverse breakdown voltage when compared to conventional pn diodes. (The reverse breakdown voltage is the maximum amount that the voltage applied to the anode can fall below the voltage applied to the cathode before a substantial current flows from the cathode to the anode.) Thus, there is a need for a Schottky diode that has a lower reverse leakage current and a higher reverse breakdown voltage.